Method of treating lubricating oils



Patented Feb. 27, 1945 METHOD OF TREATING LUBRICATING Johannes H. Bruunand Mildred M. Hicks-Bmun, I Swarthmore. Pa., asslgnors to Sun 011Company, Philadelphia, Pa.

, a corporation of New Jersey I No Drawing. Application April 1, 1942,

Serial No. 437,164

4 Claims. (6K. 196-142) The invention relates to the treatment oflubricating oils in order to improve the quality thereof.

Among the many processe which have been suggested and used for improvinglubricating oils are hydrogenation and controlled partial oxidation ofthe oil. It is well known that either hydrogenation or controlledpartial oxidation of lubricating oils will impart to the oil, thustreated, improved properties in certain desired characteristics of theoil. This improvement in the quality of the oil is most clearlyreflected in the im-' provement or increase in its viscosity index,although other properties and characteristics are simultaneouslyimproved.

We have discovered that if an oil is first partially oxidized and thepartially oxidized oil then hydrogenated until all the oxidized productsare converted to neutral hydrocarbons, the viscosity index of the oil isimproved to a much greater extent than is the case when eitherhydrogenation or oxidation is employed alone. We have also discoveredthat certain less desirable properties and characteristics which areimparted to lubricating oils which are treated by either hydrogenationor oxidation alone are not imparted to the oil when the two processesare combined in accordance with our invention.

While our improved process is applicable to and results in substantialimprovement in qual- :lty of all types of mineral oils, a particularlremarkable improvement, distinct in character as well as greater indegree, is brought about in naphthenic base oils. Oils which areextremely naphthenic in character, when treated in accordance with thepresent invention, produce oils having characteristics closelyapproaching those of the best grade of parafiinic base oils. The

l amount of improvement in the quality of naphthenic base oil that canbe efiected by meanaof our improved process increases as thhaphtheniccontent of the oil increases. The discovery that the process isparticularly adapted to the treatment of naphthenio base oils-that itdoes not merely improve the oil but imparts thereto qualities closelyapproximating those possessed by the best grade of paraffinic baseoilsis deemed by us to be specifically novel and patentable. We havetherefore specifically described the use of the process in connectionwith the treatment of such oils. However, since oils of the para'flimctype can be subjected to similar treatment with resultant less markedimprovement, the invention, in its broader aspect, is not limited to thetreatment of naphthenic base oils; 7

Briefly stated, our invention, as applied to naphthenic base oils,comprises, first oxidizing a mineral oil until the oil has asaponification number of from 8 to 12, say about 10. Any desired methodof oxidation may be employed, but we prefer to so control the oxidationthat the ratio of saponification number and acid number in oil beingoxidized is maintained at from (say) 2:1 to 3:2. During the course ofoxidation a portion of the oil is converted into esters, acids, alcohol,aldehydes, ketones and similar products of oxidation and a considerableincrease in the viscosity of the oil is effected, without, however, anyeffect on the molecular weight of the oil. The partially oxidized oil isthen hydrogenated and the partial oxidation products therein, esters,acids, alcohol, aldehydes, ketones, and similar products formed by theoxidation reaction and any unsaturated compounds present therein areconverted into hydrocarbons. This hydrogenation may be eifected in anydesired or known manner. Hydrogenation is continued until the productsof oxidation in the oil have been converted substantially completelyinto neutral hydrocarbons, as will be evidenced by the oil obtaming asaponification number of zero. This hydrogenation results in a materialdecrease in the viscosity of the oil, the viscosity of the hydrogenatedoil being at least as low as that of the oil charged to the process, andalso in a slight decrease in the apparent molecular weight of the oil.

In the case of an oil having decided naphthenic properties, the finishedproduct of oxidation followed by hydrogenation will have a lower viscosity than the oil charged to the process. This is an advantageouschange, however, since one objection to naphthenic oils is that theyhave a lower boiling range than parafiinic oils of i the same viscosity.Therefore, as a result of the change in viscosity effected in naphthenicoils treated in accordance with our invention,.we are able to producefrom naphthenic oils improved lubricating oils having a boiling rangeapproximating that of paramnic oils of the same viscosity. Even moreremarkable is the improvement in the viscosity index of an oil.

The exact nature of all the various reactions which take place in an oiltreated in accordance with an invention is not fully understood.However, the following probable explanation is oiiered as an aid to abetter understanding of our invention, it being understood, however,that we do not wish to be limited thereby. It appears that the oxidationcauses some breakdown, particularly in the compounds presentin the oil.which impart to it a'low viscosity index. The subsequent hydrogenationof the oil converts the partial oxidation products of these lowviscosity index constituents back into hydrocarbons which, however, havea substantially better viscosity .in-.

dex than the compounds from which they were;

passing air therethrough at a pressure of 145 pounds per square inch andat a'rate of 0.17 literof air per minute per kilogram of oil. At the end01"8 hours, the oil had the properties listed below in Column B of thetable. The partially oxidized oil was then hydrogenated by shaking in anautoclave in the presence of Raney nickel catalyst under an initialpressure of 2,000 pounds per square inch but which gradually dropped to1,800 pounds per square inch during the hydrogenating period'of 10 hoursand at a temperature of 300 C. The product obtained by hydrogenation ofthe partially oxidized oil was found to have the properties listed belowin Column C of the table.

Table I A B C D Naph- Same oil g fifi 011A tained after hym byhydrogencharged gs drogenating 9 ating only process tion on B 0 9.2 0 00 5.9 0 0 Hydroxyi No 0 4 0 0 Carbonyl No. 0 l2 0 0 Iodine No..... 6.615.9 0 0 Reiractive index "0 l. 5094 l. 5099 M 1. 4826 l. 4879 Viscosityat 100F. centistokes 49. G9 00. 150 30. 153 47. D18 Viscosity at 210 F.centistokes 5. l6 6. 04 4. 58 5. 53 Viscosity index 31. 80 13. 9 53 34Calculated molecular weight 341 351 330 346 It is, therefore, apparentthat the oil had been substantially improved by increasing its viscosityindex from -31.8 to +53. This increase in viscosity index wasaccompanied, asnoted above, by a decrease in the viscosity of the oiland also by a decrease in the apparent molecular weight of the oil, themolecular weight of the charging stock having been calculated as being341, while the calculated molecular weight of the product was 330.

while ior the p 'p se l fully disclosing our invention, particularmethods of oxidation and"- hydrogenation have been described above, itis to be understood that the invention is not to be limited to theseparticular methods or to the precise degree of partialoxidation that isspecified as giving the best results. The amount of oxidation to beeifected prior, to hydrogenation will vary somewhat with the characterof the oil being treated. The more naphthenic the character of the oilbeing treated, the greater is the amount of oxidation necessary in orderto effect improvement in quality of the oii'on'subsequent hydrogenationthereof. Thus. a highly naphthenic oil .swshould be oxidized until ithas a saponiflcation number-oi about 10 and an acid number or about 5 inorder that subsequent hydrogenation of this oil may effect the maximumimprovement in the viscosity index of the oil, while the maximumimprovement in the viscosity of a highly paraffinic oil may be efiectedif the oil is oxidized until it has a saponiiication number of about 3.It

shouldbe noted, however, that somewhat more oxidation of an oil'than isnecessary to bring about the maximum improvement in the viscosity indexof the oil on subsequent hydrogenation does not appear to adverselyaffect the oil but such excessive partial oxidation is merelyeconomically undesirable. Thus, we have oxidized highlyparaiilnic oilsuntil they had a saponification number of about 10 and then hydrogenatedsuch partially oxidized oil and have obtained a product havingsubstantially the same viscosity index as did the product produced fromthis same parafhnic base oil when the oil was oxidized only until it hada saponification number of about 3 and then hydrogenated. It is,therefore, apparent that with parafllnic base oils somewhat lessoxidation may be used than with naphthenic base oils in order to obtainthe maximum improvement in viscosity index. It is also apparent thatslightly more oxidation than is absolutely necessary appears to exerciseno detrimental eifects on the finished product. However, greateroxidation than is necessary n'ecessitates more hydrogenation than isnecessary, and thereiore, increases the cost of treating the oil. It is,therefore, desirable to test each oil in order to determine the minimumamount of oxidation necessary to eiiect the desired improvement in theviscosity index of the oil on such hydrogenation.

Among the advantages of our invention over presently known methods oftreating and improving lubricating oiis are the following:

There is practically no loss of oil treated in accordance with ourprocess. Unlike many extraction. processes currently employed forimproving naphthenic base oils in which a material amount of the oilcharged to the process is removed as an undesirable and low pricednaphthenic extract, in the present process the undesirable constituentsare converted into desirable and improved constituents of the finishedoil and, therefore, are not lost. The improved flnished product which isobtained from our process is substantially equal in amount to the oilcharged thereto. It should also be noted that oils produced inaccordance with our process do not have imparted thereto certain lessdesirable characteristics which are frequently imparted to oils treatedin accordance with other processes.

What we claim and desire to protect by Letters Patent is:

1. A method of improving the quality of lubricating oil which consistsof subjecting a lubricating oil stock characterizedby relatively low afree-oxygen containing gas for so limited a time as to convert a minorbut substantial proportion of the oil to products of oxidation andhydrogenating the mixture of oil and oxidation products to convertsubstantially all oxygenated material therein to hydrocarbons andproduce a substantially neutral hydrocarbon oil characterized byrelatively high viscosity index.

2. The method defined in claim 1 in which the starting lubricating oilstock is a naphthenic base lubricating oil. to thereby produce aresultant oil product having a viscosity-boiling range relationshipcomparable to that of parafllnic base 0 3. A method of improving thequality of lubrieating oil which consists of subjecting a lubricatingoil stock characterized by relatively low viscosity index to oxidationby treating it with a free-oxygen containing gas for so limited a timeas to efiect only such partial conversion of the oil toproducts ofoxidation that the oxidation oil saponification number will be between 3and 12 and hydrogenating the mixture of oil and oxidation products toconvert substantially all oxygenated material therein to hydrocarbonsand produce a substantially neutral hydrocarbon oil characterized byrelatively high viscosity index.

4. A method of improving the quality of naphthenic base lubricating oilwhich consists of subjecting a. naphthenic base lubricating oil stock tooxidation by treating it with a free-oxygen 'containing gas for solimited a time as to eflect only such partial conversion of the oil toproducts of oxidation that the oxidation oil saponification numberwill-be between 8 and 12 and. hy-

-dr0genating the mixture of oil and oxidation products to convertsubstantially all oxygenated material therein to hydrocarbons andproduce a resultant oil product having a viscosity-boiling rangerelationship comparable to that of Dar-- afiinic base oil.

J OHANNES H. BRUUN. MILDRED M. HICKS-BRUUN.

